This invention relates generally to a high intensity discharge (HID) lamp ballast and, more particularly to an improved ballasting scheme in which an auxiliary lamp is lit prior to ignition or reignition of an HID lamp or whenever an HID lamp otherwise fails to light.
Gaseous discharge lamps such as high pressure mercury, high pressure sodium, metal halide, high pressure metal vapor and low pressure sodium types are often difficult to ignite and are especially difficult to reignite immediately turn-off. Typically, up to about 15 minutes may be required in order for the lamp to sufficiently cool prior to attempting reignition. The absence of light for any period of time, whether during the initial period for ignition or reignition or due to lamp failure is, of course, undesirable.
Conventional ballasts can also include power factor correction schemes employing capacitive correction. Such schemes draw current from the utility line regardless of whether the HID lamp is lit or not lit. The current drawn by the ballast prior to the lamp lighting can be quite high relative to the current drawn by the ballast once the lamp is lit. The relatively high current level drawn by the ballast prior to the lamp being lit unnecessarily limits the number of power factor corrected ballasts which can be connected to a branch utility power line (i.e. protected by a circuit breaker).
Accordingly, it is desirable to provide an improved HID ballast for lighting an auxiliary light source whenever the HID lamp fails to ignite, reignite or otherwise fails to light. The HID ballast should also include a power factor correction scheme which increases the number of ballasts which can be connected to the branch utility power line.